This invention relates generally to motor spindle construction, and more particularly, to the construction of a motor spindle having an inner fixed stator and an outer rotor adapted to rotate with respect to the inner stator.
The invention finds particularly advantageous use in connection with the construction of motor spindles for use in magnetic disc storage drives.
Magnetic disc storage drives used in data processing applications are characterized by the dual requirements of maximum storage capacity and minimum dimensions. These requirements are particularly applicable where the magnetic disc storage drives are utilized in personal ccomputers. In order to achieve maximum storage capacity for a given diameter of a data disc and for a given total height of the disc drive, efficient utilization of the available total height by the disc pack is of great importance.
In one conventional storage disc drive, the spindle is belt driven. In particular, a spindle has a shaft with a flange at its upper end for accommodating the magnetic discs and with a pulley at its lower end around which a drive belt is trained. The drive motor is located laterally adjacent to the disc pack. This arrangement is generally used with disc drives for large discs, i.e. fourteen inch diameter discs.
According to a conventional direct drive arrangement, the disc drive motor is located beneath the spindle and the rotor of a brushless D.C. motor is directly attached to the spindle shaft.
Still another known motor spindle arrangement for disc storage drives which particularly finds use with 51/4 inch diameter discs, utilizes a spindle which is integrated with the shaft of brushless D.C. motor. The spindle is attached to the shaft end at one or both of its sides within the drive enclosure while the shaft does not rotate.
Each standard dimension magnetic disc has a central aperture of a certain standard diameter which determines the outer diameter of the disc carrying spindle. The maximum height of the motor spindle is also governed by the overall height of the entire disc storage drive which is usually standardized. When the height of the disc storage drive is totally occupied by the disc pack, the only available installation space for the motor spindle is the cylindrical bore defined in the disc pack by the aligned central apertures of the magnetic discs and the intervening spacers.
The critical operational ccharacteristics of a disc storage drive are the runup times required for the read heads to lift off the disc surface and for a certain speed to be reached and for the motor to reach operational speed, and the rotational accuracy of the spindle, the latter being determined by the arrangement of the baerings in which the spindle is mounted. The rotational accuracy of the spindle is also a determining factor for obtaining the largest possible number of data tracks per radial unit of length and, therefore, for the storage capacity of the disc storage drive. A short runup time is achieved by a high torque motor while a high rotational accuracy is received by a rigid bearing construction. These requirements have in the past, however, been impossible to achieve simultaneously since the limited installation space available for the motor spindle can be utilized either by a relatively large stator required for high torque motors or by large bearings required for accurate rotation. It would be desirable to provide construction for a motor spindle which could simultaneously satisfy both these requirements.